CO2-activation by size-selected tantalum cluster cations (Ta1-16+): thermalization governing reaction selectivity

The reactions of tantalum cluster cations of different sizes toward carbon dioxide are studied in an ion trap under multi-collisional conditions. For all sizes studied, consecutive reactions with several CO2...

Kinetics Study of Hydrothermal Degradation of PET Waste into Useful Products

Kinetics of hydrothermal degradation of colorless polyethylene terephthalate (PET) waste was studied at two temperatures (300 °C and 350 °C) and reaction times from 1 to 240 min. PET waste was decomposed in subcritical water (SubCW) by hydrolysis to terephthalic acid (TPA) and ethylene glycol (EG) as the main products. This was followed by further degradation of TPA to benzoic acid by decarboxylation and degradation of EG to acetaldehyde by a dehydration reaction. Furthermore, by-products such as isophthalic acid (IPA) and 1,4-dioxane were also detected in the reaction mixture. Taking into account these most represented products, a simplified kinetic model describing the degradation of PET has been developed, considering irreversible consecutive reactions that take place as parallel in reaction mixture. The reaction rate constants (k1-k6) for the individual reactions were calculated and it was observed that all reactions follow first-order kinetics.

Nonoxidizing heating of chip‑powder dispersions of ferrous metals in hydrocarbon atmosphere

The process of inorganic and organic components temperature transformation of metal waste into solid and gaseous products in a continuous hot briquetting muffle furnace has been studied. The composition of the hydrocarbon atmosphere formed in the muffle under conditions of limited access to the oxidizer has been determined. It is shown that the thermal destruction of the coolant oil phase proceeds according to a complex mechanism of consecutive reactions, including polycondensation, polymerization, and deep compaction with a constant decrease in the hydrogen content and ends with the formation of a coke‑like carbon residue on the surface of metal particles and an air suspension of finely dispersed carbon particles (smoke). When it is heated to hot briquetting temperatures of 750–850 °C, chemically active dispersions of ferrous metals are protected from oxidation first by a hydrocarbon gas with a density of 9.0–13.5 kg/m3, then by a pyrocarbon coating with a thickness of 0.1–0.3 mm up to the completion of the processes of pressing and cooling the briquette.

Gasification of Coal by CO2: The Impact of the Heat Transfer Limitation on the Progress, Reaction Rate and Kinetics of the Process

This paper presents the impact of thermal lag on the progress of different coal types’ gasification by CO2. The analysis was performed using thermogravimetry and numerical modeling. Experiments were carried out at a heating rate of 1–50 Kmin-1 and a temperature ranging from 383 to 1173 K. The developed numerical model enabled the determination of a true sample temperature considering the gasification process to consist of two single-step consecutive reactions. Analysis revealed that the average thermal lag in CO2 is about 11% greater than that in N2, which is related to the properties of CO2 itself and the occurrence of the char–CO2 reaction. The onset temperature of the reverse Boudouard reaction depends on the type of fuel; however, no simple relationship with the coal rank was found. Thermal lag has an impact on the kinetic parameter Aα0.5 describing devolatilization, up to 19.8%, while in the case of the char–CO2 reaction, this influence is expected to be even greater. The performed analysis proved that disregarding thermal lag may significantly hinder the interpretation of the analyzed processes; thus, TG experiments should be carried out with a low heating rate, or at the post-processing stage, a thermal lag model needs to be employed.

Small-Scale Phenomena in Reactive Bubbly Flows: Experiments, Numerical Modeling, and Applications

Improving the yield and selectivity of chemical reactions is one of the challenging tasks in paving the way for a more sustainable and climate-friendly economy. For the industrially highly relevant gas–liquid reactions, this can be achieved by tailoring the timescales of mixing to the requirements of the reaction. Although this has long been known for idealized reactors and time- and space-averaged processes, considerable progress has been made recently on the influence of local mixing processes. This progress has become possible through joint research between chemists, mathematicians, and engineers. We present the reaction systems with adjustable kinetics that have been developed, which are easy to handle and analyze. We show examples of how the selectivity of competitive-consecutive reactions can be controlled via local bubble wake structures. This is demonstrated for Taylor bubbles and bubbly flows under technical conditions. Highly resolvednumerical simulations confirm the importance of the bubble wake structure for the performance of a particular chemical reaction and indicate tremendous potential for future process improvements.

Unsteady state diffusion-adsorption-reaction. Selectivity of consecutive reactions on porous catalyst particles

The simultaneous processes of diffusion, adsorption and chemical reaction, considering the transient nature of the concentration profiles in the porous catalyst particles as applied to the analysis of consecutive reactions A → B → C, where reactant and products are subjected to diffusion limitations, are analyzed. The concentrations of the desired intermediate product B, both the average in the catalytic particles and the observed in the fluid phase, initially increase as a function of time until reaching a maximum value and then decline due to the consumption in the secondary reaction. Due to the diffusion restrictions and the adsorption effect, the observed selectivities, calculated from the concentrations in the fluid phase, are always lower than the true selectivities, which also include the amounts accumulated in the particles. Besides depending on the rates of the primary and secondary reactions, the observed yield of product B also depends on the system adsorption capacity, i.e., the relationship between the capacities of the particles and the external fluid phase to accumulate the reactant species. For a given relationship between the intrinsic rates of the primary and secondary reactions, the higher the system adsorption capacity, the lower the observed yield of B as a function of conversion. The relationship between the observed yield of B and the observed conversion of A, calculated considering the transient state of the concentration profiles in the particles, is coincident with that predicted by classical models, which assume the steady state in the particles, when the system adsorption capacity is extremely small.

Fe2+ and UV Catalytically Enhanced Ozonation of Selected Environmentally Persistent Antibiotics

The aim of the study was to determine oxidation potential of selected persistent, environmentally relevant antibiotics (Amoxicillin, Levofloxacin, and their mixture with Vancomycin) to reduce their environmental emissions. Ozonation (O3) and indirect ozonation at pH 9.5 (O3/pH9.5) were catalytically enhanced by addition of Fe2+ (O3/Fe2+) and photocatalytic ozonation in combination with Fe2+ and UV-A black light (O3/Fe2+/UV) at two temperatures using total organic carbon (TOC) and chemical oxygen demand (COD) to identify formation of by-products. Oxidative degradation followed pseudo-first order consecutive reactions. Initial phase of oxidation was more intensive than mineralisation at 21 and 40 °C: up to 57.3% and 69.2%, respectively. After 120 min mineralization at 21 °C was up to 64.9% while at 40 °C it was up to 84.6%. Oxidation reached up to 86.6% and 93.4% at 21 °C and 40 °C, respectively. The most efficient processes were indirect ozonation at pH 9.5 (O3/pH9.5) (up to 93.4%) and photocatalytic enhanced ozonation with Fe2+ and UV-A black light (O3/Fe2+/UV) (up to 89.8%). The lowest efficiency was determined in experiments with direct ozonation (up to 75.5%). Amoxicillin was the only one completely mineralised. Study confirmed that ozonation with addition of Fe2+ and UV radiation has the potential to improve efficiency of the antibiotic-removal processes. Further experiments varying amounts of Fe2+ and other experimental conditions should be accomplished to set up more general methodological approach for reduction of antibiotics emissions.

One-Pot Synthesis of Novel Multisubstituted 1-Alkoxyindoles

Studies on a one-pot synthesis of novel multisubstituted 1-alkoxyindoles 1 and their mechanistic investigations are presented. The synthesis of 1 was successfully achieved through consecutive four step reactions from substrates 2. The substrates 2, prepared through a two-step synthetic sequence, underwent three consecutive reactions of nitro reduction, intramolecular condensation, and nucleophilic 1,5-addition to provide the intermediates, 1-hydroxyindoles 8, which then were alkylated in situ with alkyl halide to afford the novel target products 1. We optimized the reaction conditions for 1 focusing on the alkylation step, along with the consideration of formation of intermediates 8. The optimized condition was SnCl2·2H2O (3.3 eq) and alcohols (R1OH, 2.0 eq) for 1–2 h at 40 °C and then, base (10 eq) and alkyl halides (R2Y, 2.0 eq) for 1–4 h at 25–50 °C. Notably, all four step reactions were performed in one-pot to give 1 in good to modest yields. Furthermore, the mechanistic aspects were also discussed regarding the reaction pathways and the formation of side products. The significance lies in development of efficient one-pot reactions and in generation of new 1-alkoxyindoles.